Wednesday, 9 November 2016

How to Live on Other Planets: Mars

No planet in our Solar System has been the focus of as much attention as Mars. We've looked for water, for life, for a place to live on.

What we've found is a cold, dry planet. It is familiar on the surface: polar ice caps, tectonic features such as volcanoes and valleys, an atmosphere and a day barely longer than Earth's.

However, it is different in every aspect. Atmospheric pressure is 1% of that on Earth. It is mostly unbreathable carbon dioxide, and does a poor job of spreading the warmth from half the sunlight we are accustomed to. Temperatures ranges from -135 degrees Celsius to an infrequent 35 degrees Celsius, averaging -55 degrees Celsius to Earth's 14 degrees. Dust storms sometimes fill the sky, but their main effect seems to be eroding the ancient geological features over a surface area equal to Earth's landmass.

The planet is also long dead. Most of the core is no longer molten, meaning that it does not spin to generate a magnetic field. Being 15% of Earth's size, it cooled down to its present state much quicker.

Habitability

Mars's thin atmosphere barely touches the surface features.

Despite its downsides, Mars is pretty hospitable compared to other planets in the Solar System. It is cold, but no unmanageably so. It has a lot of solid, traversable ground. The polar caps contain billions of tons of water ice covered by a layer of solid carbon dioxide. The soil can be used for agriculture after some preparation.

Martian gravity is 37.6% of that on Earth. It is doubtful whether this is enough to stave off the muscle atrophy and bone loss caused by prolonged living in low or micro-gravity.

Atmospheric composition.

The low atmospheric pressure means that most architecture and equipment on Mars will have to be hermetically sealed and pressurized. This imposes structural constraints and a dangerous failure mode if the colony's walls are pierced. Obtaining breathable gasses might requires energy and time: oxygen can be removed from carbon dioxide by energy-hungry chemical reactions, of through the photosynthesis of plants. Nitrogen is present at a 1.0% concentration in the thin Martian air, so it can eventually be extracted for small colonies to use as fertilizer and breathing mix. Larger colonies would need to find it in the soil, either as NO3 or NO.

The atmosphere actually helps with the cold, as it is so thin that lacks the ability to conduct heat away from the colony. It acts as an insulator. This makes dealing with Mars's low temperatures easier than on Earth, where a thick atmosphere steals heat away from buildings in Antarctica or Northern Canada much more quickly.

Mars against the Solar Wind.

The lack of a protective magnetic field is problematic to hopeful colonists. It means that every living space must have radiation shielding. This can be in the form of a layer of Martian soil layered over colony habitats. Building the habitats and covering them in red dirt is faster and easier to do than digging them into the ground.

The two best places to start a Martian colony are the poles or the equator.

The poles are vast deposits of easily accessible water. While the lower latitudes experience violent outgassing and 400km/s storms, the center of the poles have stable temperatures and terrain. Sadly, that stable temperature is -25 50 -153 degrees Celsius.

The equator receives much more sunlight, and has seasons that warm the surface to reasonable temperatures during the Martian Summer. However, equatorial colonies would be limited to where underground water deposits could be found.

Prospection

Mars is the perfect place to build a colony. Every material that could be required for building or farming can be taken from the environment without special precautions or techniques, such as on Venus or Mercury.

Mars's South Pole ices.

Compared to Venus, it trades convenient gravity, pressure, radiation protection and comfortable temperatures for greater security, ease of expansion and practical benefits such as over-land travel or surface landing.

The poles are vast sources of solid carbon dioxide and water. It is suspected that there is frozen methane too, rapidly destroyed by ultraviolet rays if they escape.

Mars soil scooped up for analysis by the Phoenix probe.

Martian soil only requires the removal of perchlorates and introduction of fertilizer to become farmable land. It can become literally dirt-cheap radiation shielding, and martian cement with an impermeable inner surface can be used to construct pressure vessels for habitation.

Iron and most metals commonly found on earth are also present on Mars. Some require digging up from the yet unexplored bedrock or from ancient volcanic veins, but they can still be considered 'available'.

However, Mars is disadvantaged when it comes to exporting raw or manufactured products.

This can be mitigated by the colonies' ability to become self-sufficient, but would hinder them if they tried to buy and import resources that cannot yet be manufactured on-site, such as processed nuclear fuel or phosphorus. This is especially important during the run-up to Mars's self-sufficiency, when more and more complex machinery is required.

There are two main causes to this disadvantage: energy and gravity.

Mars is energy-poor.

It lacks the atmosphere for reliable aerobraking. Attempting it requires specialized designs, incorporating large lifting bodies and heatshields. Earth and Venus, with their much thicker atmospheres, require less of such equipment.

Mark Watney inspecting solar panels. An essential job.

With half the sunlight, solar energy is less powerful. It is also vulnerable to dust storms that can cover the panels. While orbital solar power satellites can transmit power to the ground much more easily that on Earth (water vapor absorbs microwaves here), electricity will remain an expensive resource. Geothermal power is non-existent, and nuclear power requires advanced technology that is hard to replicate and fissionable fuel.

Bedrock elements are easily mined, but require a lot of energy to extract from their chemical compounds. The same goes for the more reactive elements, such as oxygen from carbon dioxide or iron oxides.

The second cause is Mars's position with regards to deltaV.

Liftoff, for example. Unlike Venus or Mars, it is hard to provide this deltaV cheaply through external power propulsion. Mass drivers on the ground are an option, considering that hypersonic flight is much less taxing on airframes than on Earth, but it just moves the problem around: lifting your products from Mars's surface costs 4.1km/s. If we are considering Earth is a destination, you would have to wait two years to attempt the lowest deltaV trajectory, while Venus and Mercury can attempt the same several times a year.

Rocket fuel from the surface of Mars is a good resource to export, either to missions departing from Mars, or to asteroid mining ventures exploiting the Asteroid belt. It can be made on the surface from carbon dioxide and water, producing methane and oxygen. This is what SpaceX intends to do to refuel its rockets, after they land on Mars. It is valuable if the only other source of rocket fuel is Earth, 225 million km and over 12km/s away. However, if there are colonies on other planets and asteroids, then lifting fuel up from the surface of Mars will not be competitive.

Asteroids can also provide most of the minerals and metals found on Mars without the hassle of mining it from the bedrock or deeper.

So what can Mars do?

Phobos and Deimos.

Forget the surface. Mars's greatest asset is its two moons: Phobos and Deimos.

Phobos is about 22km wide and orbits at a mere 6000km altitude. Deimos is 12km wide and orbits at an altitude of 23460km.

The two diminutive rocks have all the characteristics of asteroids captured from the depths of the Solar System. Properly used, they are Mars's key to a prolific position as the gateway of the inner Solar System.

Let's start with Phobos.The closest description would be a floating pile of rubble, loosely held together by a layer of compacted dust. It is composed mainly of carbonaceous chondrite rock riddled with ices and crevasses that might take up to a third of its volume. What is it good for? Living and lifting.

View from Phobos. Mars fills a quarter of the sky.

Phobos has a surface gravity of about 0.0004g. Riding a bicycle on the Mars-facing side is enough to fall off the moon and start orbiting Mars instead. It also means that it is very easy to dig into Phobos and excavate large volumes. These volumes can be filled with orbital habitats. These will have access to large quantities of volatiles and minerals, and the surrounding rock will provide sufficient radiation protection.

At 6000km, Phobos is also close enough to start considering orbital elevators. A cable can be dropped from the moon to an altitude of about 10km. In the simplest version, it passes over the surface at 2662 km/h. A mass-driver launched spacecraft or even a supersonic aircraft can catch up to the cable. The Martian end of the cable experiences nearly no drag, so it doesn't heat up. Structural requirements are so low that it can be built from existing materials such as Zylon. It only needs to be about 12 times heavier than the payloads it expects to receive.

Once the aircraft or pod is attached, it simply climbs up to Phobos with no propellant required. This is a 'free' 4.1km/s of deltaV.

A more advanced version has an equally long cable extending out from Phobos. The two cables rotate in opposite directions to the moon's orbit, allowing the lower end to nearly cancel its velocity, while the higher end travels at twice the orbital velocity.

The advanced version allows Phobos to 'pick up' payloads from the surface, then fling it outwards on the opposite end. At 4km/s, it can impart enough velocity to fling a payload all the way to Earth. In reverse, it can capture a spaceship entering the Martian system, and deposit it gently onto the surface at the other end.

A cable system vastly cheapens travel to and from Mars's surface, Mars's moons and extramartian destinations. Mars might end up being an even easier destination than Venus with its aerocapture or Mercury with its beamed solar power. Thanks to low surface gravity and thin atmosphere, the cables can be made from conventional materials and do not require much protection.

Deimos is a more extreme version of Phobos.

It is even smaller and higher than Phobos, but nearly identical in every other way. With a cable system, it can capture interplanetary spacecraft and lower them to Mars's surface or Phobos's orbit even more cheaply in terms of deltaV saved, energy required and structural mass involved.

So, by properly exploiting its moons instead of relying only on the surface, Mars becomes a very inviting destination for spacecraft. While it lacks the energy to produce or refine products cheaply, it can compensate by providing rocket fuel and sending off the products to other destinations at greatly reduced deltaV cost.

The Martian Colony

The Martian colony won't look like much from space. No open domes, no large exposed surfaces. Every building is covered by a dusty layer of martian soil to protect its contents from radiation. Early settlements would have a field of auto-wiping solar panels placed far away enough to prevent them being damaged.

Since buildings are pressurized, they will have rounded, smooth shapes to prevent angled weakspots cracking under strain. They will also be relatively 'clean', as in little clutter marrs their exterior surfaces. Anything left outside, like an antenna or a door, will be subject to extreme temperature variations that if not causes them to fail, will reduce their useful lifespan.

Most components are kept under a mound of Martian soil.

Thanks to the ease with which new buildings can be constructed, colonies might appear dis-organized. They are able to expand in steps without de-stabilizing the entire project. A floating colony on Venus must match its lifting capacity with the mass of the habitats, and a rotating space station must balance new weights with ballast on the opposing side. On Mars, it can be as simple as claiming new land and hooking the new building up to life support.

However, there will be notable differences. Breathable air takes energy to create from local resources, and energy on Mars is expensive. Every attempt will be made to conserve air. For example, vehicles will be docked directly with a building's airlock, instead of sitting outside. It would only involve a single airlock cycle that way, instead of two if colonists had to go outside then enter the vehicle.

Vehicles might not be human-piloted near habitats, and driving in general would be tightly regulated. A collision with a habitat could mean the instant depressurisation of its interior.

The largest volumes of a Mars colony are dedicated to farming. They would resemble a sort of artificially-illuminated greenhouses, with rows of algae and vegetables growing in drip-fed batches.

Tunnels between habitats are the safest way of travelling around the colony. They would replace the roads common to Earth's inner cities. Outdoors activity would be restricted due to radiation concerns. Overall, the colony would appear uninhabited from the outside.

On the inside, the habitats would appear rather cramped. Due to pressurization reasons, rooms are small. The colony would appear to a colonist as a succession of 'bubble-rooms' separated by tunnels and airtight hatches. New arrivals would bump their heads constantly on the low ceilings, as they adjust to low gravity.

The longest distance to travel would be between the spaceport and the habitation spaces, for safety reasons. If the colony is of the industrial type, it might instead employ a mass driver or a landing strip for supersonic tether-to-orbit aircraft.

Travel between colonies would require long road-trains, as air travel is no practical. The alternative would be some sort of suborbital hopper, probably reserved for transporting people instead of goods. Railroads would be possible, but the rails would have to survive the temperature extremes between night and day.

Dangers

Most dangers arising from living on Mars are caused by the fact that it is a cold, low-gravity desert.

Rather familiar with the dangers of living on Mars.

Depressurisation is just as dangerous as in orbit. The thin atmosphere won't slow down micro-meteorites much, so an unexpected puncture of habitats has to be accounted for. A layer of sealing fluid might surround habitats.

Radiation is greatly reduced through appropriate shielding, but colonists are expected to work outside in pressure suits. These will have much less effective radiation protection, so damage will accumulate and might lead to a much higher cancer rate than on Earth.

The low gravity can cause long-term problems with bone less and muscle atrophy. These cannot be compensated for by short stays in a centrifuge. They require hormonal treatment and possibly genetics work to adapt colonists to being born and raised on Mars.

On Phobos or Deimos, the risks are a bit different. They are unstable, and it is likely that large pieces of rock will start moving if colonists remove the ice 'filler' in between them. Long-term stability of the moons has to be balanced against the growth of the colony. With a tether system, there's always the chance that the cable will be severed by a collision, and end up loose. They could whip around and strike the moon's surface, or detach and launch debris into Martian orbital space. The cables will not be as large or devastating as a terrestrial Space Elevator, but there will be less atmosphere in the way to slow the descent of debris to the surface. On Earth, debris from a space elevator will be slowed down and hit the ground at near the terminal velocity, which is just under Mach 1 for the largest pieces. On Mars, the same pieces can strike the ground at close to the orbital velocity, which is several kilometers per second. Even with smaller pieces, they can end up being more devastating.

Evolution

In any colonization attempt, Mars is likely to be the first candidate, and the only option for a long time.Early colonies will likely be research outposts, with the only commercial-industrial activity being the production of liquid methane and oxygen rocket fuels. The fuels can be used to return landers to orbit, or shipped to spacecraft going even further than Mars. An example of the latter will be asteroid mining operations. Colonization efforts will focus on the polar regions at first, as they offer vast quantities of volatiles. The reduced sunlight and consistently low temperatures will have to be compensated for by larger solar panels.However, industrialization, both for supplying a self-propagating colonization effort and for supporting an interplanetary economy, is best done around the equator. The deltaV cost to reach orbit and leave Mars is significantly lower than from the poles, and greater sunlight means cheaper electricity. The transition from polar colonies to equatorial colonies depends on a reliable transport system. It will have to cross a 5500km stretch of land, about the distance from London to New York. Flight is unwieldy, and suborbital hops too expensive. The growth of martian colonies follows a snowballing model. As it develops, it can produce more and more rocket fuel and machinery. These will be cheaper to use than similar products shipped from Earth. Cheaper products means that investors can do more with the same investment, leading to growth and greater demand for martian products. These products can be metals from the asteroid belt, moved by martian rocket fuel, or more colonies on Mars.Phobos and Deimos are the keys to Mars's maturity as an industrial power, as it will drastically reduce the deltaV cost of travelling to or from Mars. It will supplant Earth as the better investment for space-based industries. Ultimately, Mars will end up serving as the starting point of further colonization or resource exploitation efforts in the Outer Solar System. Leaving for Jupiter from Mars will be cheaper than doing the same from Earth. As colonization continues, the population on Mars will become a consumer base in its own right. Corporations might consider selling their produce directly to Martians, instead of shipping it to Earth. A permanent population on Mars will have to resort to more drastic measures against bone loss and muscle atrophy, and the increased radiation risk. Its colonies will develop into vast network-cities, where every point is accessible through shielded tunnels without ever having to step outside. This reduces exposure to radiation.Land travel will start using railways instead of slower roads. Thanks to the near non-existent atmosphere, even conventional technology can push trains to supersonic speeds without the need for Hyperloop-style vacuum tunnels. It could end up being cheaper than flight.

A potential Martian space elevator.

Orbital space stations will flourish around Mars, with miniature cable systems to reduce the cost of reaching them. Their main function would be to tend to interplanetary spaceships so that they do not have to set down on the surface. A secondary function would be to create artificial gravity environments where colonists can compensate for bone loss and muscle atrophy. If Mars has to compete with colonies on other planets, such as Mercury or Venus, it would have to find ways to remain competitive despite its energy disadvantage. A historical perspective can help with worldbuilding this aspect of its colonization. Modern 'developed countries' were initially industrial, but transitioned in the past century to a services-based economy, where the wealth and infrastructure of their industrial past is optimized towards creating wealth without any physical products in play.

Interesting take on Mars. I am generally not a big fan of Mars for the same reasons you outlined as disadvantages, but I suppose there will be enough institutional inertia to make Mars an attractive destination for the first colony site anyway.

Builders on Mars might actually have it a bit easer than you think, digging a large branch and then building a barrel vault out of locally produced brick inside provides the structure and structural strength for fairly large spaces, and the trench can be backfilled for further protection after the vault is completed. Vaulted spaces can actually be quite complex and beautiful, as the interior of any gothic cathedral will demonstrate.

Indeed, after the initial quick and dirty quonset hut type vaults are inhabited, I can see a trend towards really large vaulted chambers, with apartments along the sides and the huge central atrium to provide a sense of space (each apartment would still be self contained in the event of an emergency, but the vault itself will be a strong masonry or concrete structure and covered over with several metres of Martian soil). Tunnels between the vaults would eventually be extended into hyperloop or similar "intercity" lines between colonies.

Still, that pesky gravity and atmosphere will put a lot of negative pressure on the colony economy, not enough to be really useful, but still enough to cause problems and increase your costs compared to the Asteroids or Mercury. I could almost see Mars becoming a sort of dumping ground full of half baked investment projects that never quite pan out, while the smart money gets invested in the 3He Skyhooks over Saturn and similar projects.

I see Mars as becoming a 'rust belt' in the larger Solar System economy, as early industrialization is superceded by similar efforts on planets where more energy is available or it is easier to live on.

The situation might change if both genetic modification and fission energy becomes widespread.

For example, if space colonization is preceded by some sort of treatment that makes colonists immune to the debilitating effects of low gravity, and thorium reactors are supplied for cheap, then Mars becomes attractive again. On the other hand, methalox fuel will be less valuable to spacecraft with nuclear power, but it can be compensated for by boosting hydrogen to orbit instead.

I doubt hyperloops will be needed. Overland transport can very well be done on the surface: staying an hour inside a shielded train shouldn't be bad enough that a tunnel is needed.

Now that I think of it, if we are agreeing that Mars is going to be a "Rust Belt" planet, then just why is Earth sending a space force to attack or subdue it?

And where are the Martians getting the money and equipment to put up armed resistance?

Earth could quite easily take over Mars spending the same amount of money in infrastructure and other investment on Mars itself (or offering billions of Solar Dollars worth of "Freestuff" to gullible Martian voters) as they would building a space fleet.

I suppose there are also scenarios where Earth uses Special Operations Forces, Psyops and other indirect means to subdue colonies, while the colonies fight back using the principles of 4GW in protracted insurgencies.

I always thought of the Mars vs Earth conflict as retaliatory:Mars would surpass Earth in profitability per kg in space, and Venus would absorb all post-asteroid mining operations (refining), leaving Earth with no direct source of space-based income, and forced to import extraterrestrial products at premium products.Mars and Venus could strike up a consortium which could squeeze bloated Earthlings harder than OPEC did in 1973. Earth would feel threatened, and forced to use the one asset it owns that Venus and Mars cannot match: military power.Building missiles instead of solar panels cuts into profits, so Mars never created a space navy and hopes that concessions and bribing would keep Earthlings quiet. The diplomatic solution can only go so far, when Martian corporations suddenly realize that countering military force with their own deterrent might end up making more money in the end.

Earth, threatened economically and soon militarily, retaliates. It attacks Mars. Mars concedes immediately, diverting its war effort into a guerrilla force and relying on its Venus/Asteroid allies to shake off Earth's hold on the Solar System indefinitely.

At least, that's the scenario I think would justify this sort of conflict.

Realistically, space industry produces things for space. In terms of raw materials or technology, Earth is going to be the centre of the industrial ecosystem for the Inner solar system for centuries. Even in terms of scientific knowledge, Earth simply has a much larger pool of researchers, scientists an technicians than the early colonies will be able to muster.

There is one thing which will draw a massive reaction from Earth, however, and that is the perceived threat of high speed objects bombarding the planet. I can see the real thrust of space control and militarization being to prevent the unauthorized movement of asteroids, spacecraft and eventually any object that could be in an Earth crossing or intersecting orbit. The Chelyabinsk meteor was only @ 20m in diameter, yet exploded in the upper atmosphere with a yield of @ 500KT (most strategic nuclear weapons today are thought to average only 300KT yield). Objects moving on fast interplanetary orbits will have comparable yields as a lower boundary, and the fastest any object can move in a free trajectory in the Solar System and still remain bound to the Sun is 72 Km/s, with correspondingly higher yields.

Depending on how properly paranoid people become over this threat, there may be an interlocking series of Space Traffic Control boundaries, with the very explicit threat that anything deviating from the assigned and prescribed orbital parameters is going to be destroyed as rapidly and as completely as possible. In this sort of setting, any hint of a "Stealth" technology could be taken very badly; having a huge spacecraft impacting at interplanetary speeds without warning would be perhaps the deadliest threat to any polity, free flying colony or other inhabited structure or body possible, and people will go to great lengths to prevent that from ever happening.

In the first post of the series (Mercury), I stated that I would consider colonization without an Eath-centric view. If we take Earth out of the picture, we might be able to consider the planets more objectively.

Artificial gravity with orbital space stations? You do know you can just tilt the floors of a centrifuge wheel located on the Mars surface (or underground) so the net gravity vector is still normal to the floor. Though if you have to do that because 1/3 G isn't enough, I'm uncertain what remaining advantages Mars has at all. Especially compared to an asteroid or even one of the moons of Mars.

Dunno how useful they'd be, or how bad the fallout would be with "clean" bomb designs, but without an atmosphere to contaminate or a biosphere to move the fallout around, it would be a lot easier than on Earth.

The reason we're afraid of nuclear fallout on earth is because it can invisibly go basically everywhere. Living creatures carry it, the wind, the rains. If everyone has to live inside hermetically sealed environments, what danger does the fallout even pose?

If radioactive dust gets on a space suit and you then go inside, ok. But the most common way to use suits would probably be the style where they dock at the back and stay in near vacuum anyways. And you can always spray CO2 on them to brush off the radioactive dust, and in a future world of Mars explorers, tiny radiation detectors would probably be embedded in every airlock, habitat, tablet - everything. You'd probably get an alert right away the moment a significantly radioactive particle lands on your space suit.

The second danger is direct gamma ray exposure, but nuclear fallout will rapidly cool and minimize this risk within weeks. And the exposure only happens to people and equipment in direct line of sight of the radioactive crater. (and again, there would probably be an immediate warning on a space suit used by a Mars colonist and some kind of direction marker to point to the approximate direction the rads are coming from)

So really the only problem is you can't blow a hole in the ground with a bomb then try to live in the radioactive walls of the crater. Not without then chewing off 10cm or so off the walls with a mining machine and dumping all the debris somewhere away from the colony.

I think the lack of biosphere or breathable atmosphere solves a lot of problems regarding nuclear fission. You could probably also operate nuclear fission power reactors with minimal shielding - just set up the reactor core in a tunnel somewhere and maintain it with robots only.

I know this is off topic and not directly related to Mars, but I was wondering about the possible effects of interplanetary travel that would result from a Martian colony. Since Mars has less gravity on Mars, humans living on Mars without gravity supplements will inevitably develop less bone mass. I was wondering what would be the chances of a Martian born human being able to go to Earth (walk on its surface)? Would it be impossible without some genetic enhancement or exoskeleton assistance?

People that travel in space regularly will have an easier time adapting to Mars than to Earth when they land.

Reports on whether 40% of normal gravity, like on Mars, is sufficient to maintain bone mass are inconclusive. If it is sufficient, then some hormonal treatment and calcium supplements are all that are needed.

If it is insufficient, Martian colonists can build themselves large, complicated and risks drum-colonies that rotate at an angle to the surface to simulate 100% gravity, or stay for long periods of time in orbit, in spinning space stations.

Of course, there's always the option of astronauts or colonists genetically modified to be less sensitive to lower gravity. It could end up being a very cheap and simply option, if the technology is properly developed.

Thank you for replying! I find your information to be useful and very valuable. However, this explanation also puts me on a tangent. Would it be possible to use some sort of exoskeleton system as a useful aid for those adjusting to planets with a gravity noticeably stronger than what they are used to?

You are welcome. Please try to create an account, as it will greatly reduce the risk of a comment being marked as spam and disappearing.

All tangents are welcome, as they can expand the discussion.

Exoskeletons will certainly be useful, but not in our Solar System. Nowhere is there a solid surface with higher than 1G. You'd have to invent a super-earth type planet in a fictional solar system for exoskeletons to be used that way.

Don't be sorry for asking questions. I invite everyone to do so. Are you aware of the Rocketpunk manifesto blog? Like there, the main focus of these posts is providing material for lively comment threads.

Matter Beam: "Reports on whether 40% of normal gravity, like on Mars, is sufficient to maintain bone mass are inconclusive."What reports?SFAIK there is no data on the effects of staying in gravity between 0g & 1g for more than the few days some Apollo astronauts stayed on the Moon. So Lunar gravity *could* be enough for good health or even Venus gravity might not be enough.Are you aware of some information on the topic that I have missed?

To get such data I would like to see a moon base built & a rotating habitat that gives martian level gravity..Jim Baerg

Sorry, I should I have used stronger words. We just don't know the effects.

However, we can guess at them. Bones are continuously recycled by osteocytes. The hydoxyapatite (bone material) is eaten up and reformed. The mechanism of bone loss in microgravity is that reduced tension on the bones causes the breaking down to exceed the re-making of the bone material. There is a net loss in bone mass.

This causes weaker bones that are a big problem upon returning to normal gravity. It also causes hypercalcemia. The closest terrestrial condition is found in immobilized patients, which experience all of the same symptoms up to and including fluid redistribution and weakening of cardiac muscles (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3871450/). The majority of these symptoms are treatable (low-calcium food, aerobic exercise, kidney stimulants) and some aren't really a problem if the colonists don't intend to return to Earth...

All in all, I think there is sufficient data to support the theory that the body's response to different gravity levels is analog and not digital: it doesn't completely collapse, it just adjusts to the new environment.

All in all, I don't think partial-gravity research could justify building a moon base. Eventually, we might run a spinning habitat on the ISS at lower-than-intended RPM, but other than that, it might be more cost effective to just design the Mars mission with less intermediate steps.

So, I have some questions, I was hoping you'd be able to answer regarding Mars.

1) Would the same kinds of mass drivers utilised for sending payloads into orbit also make effective (improvised) anti-orbital defence? Similarly, would Mars' atmosphere be thin enough to make a laser weapon viable for use against potential invading forces?

2) Going from the Phobos tether concept, you mentioned supersonic aircraft could be able to reach the business end of the tether. Would these craft look similar to planes and/ or shuttles we have on Earth or would they be different? My reasoning is that Mars' atmosphere is incredibly thin, and I don't know enough about aviation to know if it would still be enough to provide lift.

3) Going for the idea of Mars and X going to war, would it make sense to begin constructing colonies going further underground by digging out the rock (Kind of like some real proposals for using drones to build colonies before we even get there)? Would it be practical to have ever-deeper networks of rooms and corridors that are definitely-not nuclear bunkers?

4) To piggyback that last question, would large cavernous spaces akin to Ceres (The Expanse), the Citadel's presidium (Mass Effect) or a less-extreme version of this (https://www.artstation.com/artwork/n1w51) Titanfall concept art with artificial skies and less-cramped areas be practical? I'd assume that for Mars cities (as opposed to smaller colonies and outposts), you'd eventually want areas where people can run, play sports, go for walks and simply just have a less claustrophobic space for recreational purposes.

5) You said that equipment would not be left out overnight if it can be avoided as it could make it unusable due to temperature fluctuations. In that case, how would communications work? Both for larger satellite dishes designed to recieve communications from orbiting spacecraft and smaller radio antennae. Would they simply require constant maintenance as an unfortunate consequence of wanting communications?

I'm trying to go for a full-on Mars city underground rather than just a simple surface colony, but I'm beginning to go into the visual design of it (I'm going for games) so I'm hoping to go for something visually interesting as well as plausible.

Great questions! I'm sorry for delaying on posting the next entry in this series.

1) There are generally two types of mass-driver-into-orbit concepts: fast and slow. Fast mass drivers accelerate dumb payloads at 100G+ within a short distance. Slow mass drivers are extremely long to reduce the acceleration to about 1-3G.

Fast drivers are short enough that you can swivel them around to shoot into different inclinations. However, the payload must be small and cannot have fragile electronics or humans on-board. They're great for sending rocket fuel up, for example, but not guided warheads. They are the best suited for weapons.

Slow mass drivers will resemble massive tunnels: fixed direction firing of conventional payloads. They will be so big and long that they'll become very vulnerable to counter-attack. If they are defended, however, they become a very effective defense. Not by shooting down targets, but by essentially bringing your planet's industrial production into orbit. Over time, you will put up several time more tons of material and equipment into space than your opponent could ever transport from Earth or elsewhere.

Laser weapons love Mars. One idea I had for defending a colony is to have a space warships's laser generators be de-orbited and hooked up to the colony's electrical generator. This way, it will fire without stopping, at higher MW ratings than possible before!

2) On earth, supersonic aircraft are 10000Isp+ rockets that have a maximum speed. On Mars, they are not needed. A SkyHook design can dip into the atmosphere and slow down to 0m/s relative to the ground without heating up at all! It is practically free payload delivery into orbit.

Mars' atmosphere is about a hundred times thinner than ours on the ground: you can go 100 times faster, or need 100 times bigger wings. Or, ditch the wings and go supersonic over land.

3) The colonies underground can be justified by radiation protection. If all the living quarters are underground, they don't need any insulation for heat differences between day and night either. They'd make a perfect starting point for underground bunkers.

4) The biggest expense involved with asteroid basis is putting the asteroid in the orbit you want. With Mars, you have Phobos already on your doorstep. Literally scoop up the iron and water you need to start building and construction can begin! I think an asteroid colony will not live INSIDE the asteroid, but AROUND it.

5) A big metal dish is much tougher than a car or a space suit - so you can have basically all your communication equipment behind protection, with only the 'antenna' sticking out. Also, many types of radar can penetrate through walls and radiation shielding, so they allow communication with nothing exposed.

For the visual design, I'd suggest:-Industrial above ground, living quarters underground.-Everything bulbous, spherical and round to support pressure efficiently.-Industrial areas might be un-pressurized, and can have sharp edges and dim lighting as people aren't supposed to be there. -Colonies would be built around one distinctive feature. Maybe an orbital railgun with hundreds of kilometers of supersonic trains leading up to it all around, or a glittering solar array that feeds hectares of underground plant farms!

Thanks for the response! However, I want to clarify some of my questions;

For Q2, I meant how you'd get from Mars surface to the skyhook itself - how would these kinds of Mars atmospheric craft look like for transferring peoples and cargos from the surface to the tether?

For Q4, I more meant if you could build those sorts of areas in an underground city on Mars? I was considering that the most luxurious/ well-off city would have a sort of commons area with a larger area like that image I linked for recreation and whatnot.

Thanks for the response though! I pretty much have my style for the more Earth-based stuff down (More a mix of Titanfall/ Halo stuff) and I've been vaguely using Elite Dangerous for a lot of my inspiration in regards to stations and planetary outposts (The smaller in-game space stations and planetary bases, at least).

The SkyHook reaches down to a few meters above the surface. It will stay motionless for a couple of seconds, hanging in the air, before it accelerates straight up and away. All you have to do is hook up to it.

On Earth, this is tough on the tether, as it would have to travel at Mach 25 through the air before and after stopping over the ground, so they make it only dip into the upper atmosphere, and have a larger relative velocity (Mach 8 for example). On Mars, the atmosphere is not a problem.

On Mars, just having a large open area is a sign of wealth. Pressure is harder to contain in one big bubble or habitat, compared to multiple small spaces. You'd need large amounts of material. If you want a big, sun-lit space like in the picture, you need expensive transparent ceramics or quartz that is coated with anti-UV protection.

Just one note of caution on using video game level designs for inspiration: their first objective is to be a balanced map for gameplay. They make sacrifices to realism to look interesting or be fun, such as massive sewers or ceilings so tall no player could touch them.

If interested, I've been pretty much having a certain Mars faction slwoly building up it's military in preparation for war, but covertly - nuclear/ orbital weapon bunkers disguised as just regular undergorund construction, laser weapons built underground in silos that won't emerge until needed (Though this one has been having som issues that don't get solved until they get the aid of another faction) and reconstruction of existing mass drivers to turn them into improv weapons.

Also, as a note on lasers, would it be acceptable/ feasible to say that lasertech has existed for decades but has never been used in warfare simply because it was too inefficient and the energy required to power them too great to make them worthwhile aside from near areas like Mercury where Solar power is pretty much infinite? Part of my main thing is that when the big war breaks out, one of the groundbreaking technologies introduced is laser weapons, and to follow the war as this laser technology is introduced throughout the system and changes the face of space from primarily missiles and rails to more energy weapons. For this, I'm having fusion as a new/ very recent technology to help facilitate why the energy to power such a weapon is now available. Also better materials science allowing for more efficient heat radiators compared to the last war.

Your approach is quite correct- a military force on Mars would be crushed if it revealed itself too already. Also consider that not everyone would support their actions: such a military force's first victims would be Martians themselves....

Laser tech for most purposes would be of rather low wavelengths. Infrared mostly, microwave if you're trying to get through thick atmosphere, optical if you want to communicate long distances. They only require cheap materials to focus them, such as aluminium, and easy to make generators.

However, for warfare, you'll want short wavelengths (like ultraviolet) and expensive generators, like the Free Electron Laser.

Maybe you can have the enemy, like Earth, have access to advanced lasers, but the technology is stolen and retro-engineered underground, on Mars. When Mars attacks, it is suddenly on an equal footing with the more advanced enemy.

You make sense in most of your post, but I have some comments on the points I disagree with.

"Colonization efforts will focus on the polar regions at first, as they offer vast quantities of volatiles."

Actually I don't think so. Doing a Google search for images for 'Mars water map' I get some maps that show equatorial regions with substantial soil water (about 10%) eg: http://www.wikiwand.com/en/Water_on_MarsSo there is plenty of water in some regions that are easy to get to from the Phobos tether.

Re: solar power for a Mars colony.Night is a major drawback for solar power on any planetary scale body. Use nuclear for baseload supplemented by solar only to cover daytime peak in demand. A nuclear reactor sufficient to power an initial base wouldn't be terribly massive especially if the shielding is local regolith & the reactor is started only after being covered with regolith.

OTOH solar is good for things in orbit since they never spend very long times in shadow, & even far from the sun, curved mirrors of aluminized plastic to concentrate sunlight would be cheap even by the km^2.

-The first colonization attempts will happen before a phobos tether is in place, so staying on the equator due to favorable orbital mechanics is less of a concern.

-10% soil water is harder to access, and requires more substantial preliminary steps, than just scooping up ice and melting it. For the first colonies, this might be a issue.

-There is plenty of CO2 in the Martian air, but it is so thin that it will hard to collect and condense large quantities of it. Being on the poles has the advantage of handing over the CO2 freely and in large quantities, to produce carbohydrates or carbon monoxides for cheap rocket fuel.

-A colony at the right latitude will have many more hours of sunlight per day than the equator, at least for the first 'season' during which it is being set up. Nuclear power is an incredibly useful tool, but relying on it strictly limits how far the colony can expand to how many reactors were brought from home. Also, something like a carbon-carbon battery (http://newatlas.com/dual-carbon-fast-charging-battery/32121/) built out of local materials might provide the power storage to eliminate the night/day issue entirely.

Of course, in the long term, your suggestions are valid. Staying on the equator makes rocket launches cheaper and tether deliveries feasible. Orbital solar power would supplant panels that run rings around the poles for continuous sunlight, and overland transport makes gathering polar volatiles and delivering them to the equator easy...

Exporting Venusian atmosphere elsewhere has been seriously studied as a possibility for allowing colonization. Moving it to Mars is an option...

but it would not be a practical option. The same effect can be done for less energy by cooling Venus below to freezing point of Carbon Dioxide, then trapping the ice underground. This removes CO2 from the air and reduces overall pressure. Cooling is as simple as blocking sunlight over a large surface area of the planet, starting with the poles.

The reverse can be done on Mars. It has a lot of carbon dioxide and water trapped in polar ices. By focusing sunlight on the poles, the ices can be turned back to gas. The greenhouse effect is cumulative and soon you won't need to focus sunlight. The rising temperatures melt the ices on their own.

There is one downside to this method, however. If the temperatures are left unchecked, Venus's trapped CO2 will escape again, and Mars will freeze on its own. Physically moving the atmosphere is extremely difficult, but would be a final solution.

Would we need to?Is there any data on how much nitrogen is in the Martian regolith, such as in the form of nitrates? Could there be enough to make a reasonably thick atmosphere?

If we did the hard part would be getting it off Venus. 'Dumping' something onto a planet is just a matter of putting on a collision course with the planet, preferably in small enough chunks to not be disasterous.

@Jim Baerg:It takes 571kJ/kg to convert solid CO2 into gaseous CO2 (and vice versa). It takes more than 172MJ to move one kilo from Mars surface to Venus surface, according to these tables: http://www.projectrho.com/public_html/rocket/appmissiontable.php

Even if we use aerobraking to shave off a few km/s from the deltaV required, the difference in energy, and therefore cost, of actually moving things around is huge.

Mars has enough nitrogen locked up in certain rocks to give a thick Earth-like atmosphere. The rocks have to be superheated to start thermally decomposing and releasing nitrogen, which is much harder to do than simply letting green houses gasses fill it up with CO2. The quantities involved are quite huge too. You'd need 2.5 times more gas than on Earth to compensate for the weaker Mars gravity. This means a quantity of nitrogen equivalent to about 10000 trillion tons.

If you still want to do this, then the best way is to just freeze the Vanusian gasses and send them as big ice cubes or comets to crash down onto Martian poles. This requires the lowest amount of 'spaceship' per 'gas'. The kinetic energy released upon impact serves to heat back to the gasses into the new atmosphere.

If your objective is simply to have a freighter making regular trips between Venus and Mars for stories to take place in, then it is best to forget transporting raw materials. It is hard to justify a terraforming process that involves both planets, and its even harder to sell the gasses because the atmospheres are so similar in composition.

If you still want a terraforming angle on the story, you could exchange terraforming machines and products. Because of how much sunlight, nitrogen and carbon dioxide Venus has, it can easily produce chemicals such as fertilizers or aramid fibers or even amines, resins, plastics, explosives and so on for commercial purposes.

You can't just transport these in big blocks of ice, so more freighter-like spaceships are needed.

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